Comment by omoikane
For youtube shorts, replacing the "shorts" in URL with "watch" will give you the usual interface, for example:
https://www.youtube.com/shorts/GqkmtcirwYA -> https://www.youtube.com/watch/GqkmtcirwYA
But actually I see that seek bar is already available in youtube shorts. Maybe it's a recent change?
YouTube shorts does have its own progress bar, but it's proprietary and kept out of view and so it doesn't allow the user to tell the length of the video at a glance.